MWE for gregorio-project/gregorio#1188

mwe.lua

local EXCLUDE = {
  ['.notdef'] = true,
  ['.null'] = true,
  notdef = true,
  nonmarkingreturn = true,
}

Mwe = {}

function Mwe.emit(csname)
  local glyphs = font.fonts[font.id(csname)].resources.unicodes
  local ignored = glyphs['___magic___']
  local first = true
  local odd = true
  for name, cp in pairs(glyphs) do
    if cp >= 0xe000 and not EXCLUDE[name] then
      if first then
        first = false
      elseif odd then
        tex.print([[\hline]])
      end
      tex.sprint(string.format([[{\scriptsize %s}&{\%s\char%d}]], name, csname, cp))
      if odd then
        tex.sprint([[&]])
      else
        tex.print([[\\]])
      end
      odd = not odd
      if odd then break end
    end
  end
  if not odd then
    tex.print([[&\\]])
  end
end

mwe.tex

\documentclass[12pt,a4paper]{article}
\usepackage{fontspec}
\usepackage{libertine}
\usepackage{longtable}
\directlua{dofile('mwe.lua')}

\font\greextra = {name:greextra} at 1000000 sp\relax

\begin{document}

\begin{longtable}{lc|lc}
  \directlua{Mwe.emit('greextra')}
\end{longtable}

\end{document}